a) Field of the Invention
The invention is directed to a cutting chisel holder with a cutting chisel which can be clamped in, particularly a rotating drill head which is adjustable in a fluidic manner.
b) Background Art
DE 34 33 793 Al (FIG. 3) discloses a rotating drill head with a tool carrier which is precisely adjustable transversely to the axis of rotation and has a wedge or key carrier which displaces the tool carrier transversely relative to the axis of rotation. The tool carrier, which forms a displacing part, is associated with an additional displacing part. The tool carrier and displacing part have sloping surfaces which face one another and are pressed outward by the key carrier. The tool carrier and displacing part are accordingly moved outward symmetrically in opposite directions in order to counterbalance occurring centrifugal forces with respect to the axis of rotation.
However, due to the multitude of parts sliding against one another, the mechanical operating means is subject to high friction so that it is not possible for such drill heads to meet the demand for a quick adjustment of the cutting chisel to produce inner cylindrical surface areas with accurate dimensions and minimum deviation (roughly 500.mu. to 1,000.mu.) from an exactly cylindrical surface area.
Further, a precisely adjustable drill head is known in which the driven member is a plate having projections and resting thereon. A tappet situated in an eccentric bore hole of the boring bar rests on the side of the plate which faces away. When acted upon in the axial direction, this tappet causes the boring bar, which has a thin and a thick wall due to the eccentric bore hole, to be stretched along its thinner wall so that the boring bar swivels toward the thicker wall and, in doing so, impresses upon the cutting chisel a virtually axially vertical advancing motion in the .mu. range transverse to the axis of rotation (see U.S. Pat. No. 3,007,356, FIG. 2).
Since the tappet contacts the plate eccentrically, the plate and tappet form a lever gearing which is unbalanced when deflected and is likewise subject to repetitive friction. Further, the tappet is acted upon obliquely as a result of this construction and accordingly experiences lateral deflections which lead to jamming of the tappet in the bore hole. Frictional and clamping forces prevent such a drill head from following slight changes in pressure whose effect does not exceed the frictional forces, and when larger forces occur the cutting chisel position cannot be associated with the control pressure in a reproducible manner, so that different cutting chisel positions result under the same control pressure, depending on whether it is falling or rising.
To prevent troublesome frictional forces and maintain the desired stiffness of the mechanical operating means, it is known to construct the drive member and boring bar in one piece (see DE 39 29 472-Al, FIG. 1).
To this end, the drill head includes a flat rotating part having a circular cross section and divided into two portions by an eccentric recess or groove, namely into a portion forming a thin plate and a portion forming a thick plate, which portions are connected with one another by the round, off-center portion formed by the groove. The relatively thin plate resulting from the groove is springing or resilient relative to the comparatively thick plate and simultaneously forms part of the compression motor, whose rigid base forms the thick plate or disk. In addition, the thin plate has a continuation which faces away and has a cylindrical outer surface area in which a piston shaped continuation engages, the latter being constructed in one piece with the boring bar. This piston-shaped continuation forms the driven member and is securely connected with the thin plate by screws. Due to the eccentricity of the remaining portion between the thick and thin plates, a change in pressure of the pressure medium supplied to the compression motor results in a driven path in the .mu. range determined by the path of the driven center of gravity of the thin plate relative to the thick plate.
With the exception of the construction according to DE 34 33 793 Al, FIG. 3, these constructions of drill heads have the disadvantage that the boring bar forming part of the drill head is out of balance when deflected. At very high speeds of the drill head, which can reach 8,000 r.p.m. and more, this unbalance can generate forces high enough to overload the bearings of the drill machine to which these forces are transmitted. Apart from this, such unbalance works against the reproducible adjustment of the boring bar.